• Restorative Dentistry and Endodontics
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• v.37 no.1
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• pp.16-23
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• 2012

Objectives: Present study was undertaken to investigate the crystal growth onto synthetic hydroxyapatite (HA) seeds in pH 4.3 and pH 7.0 supersaturated solutions with different fluoride concentrations. Materials and Methods: 8 groups of pH 4.3 and 7.0 calcium phosphate supersaturated solutions were prepared with different fluoride concentrations (0, 1, 2 and 4 ppm). Calcium phosphate precipitates yield crystal growth onto the HA seed surface while solutions flow. For evaluation of crystallizing process, the changes of $Ca^{2+}$, $PO{_4}^{3-}$, $F^-$ concentrations of the inlet and outlet solutions were determined. The recovered solid samples were weighed to assess the amount of minerals precipitated, and finally determined their composition to deduce characteristics of crystals. Results: During the seeded crystal growth, there were significantly more consumption of $Ca^{2+}$, $PO{_4}^{3-}$, $F^-$ in pH 4.3 solutions than pH 7.0 (p < 0.05). As fluoride concentration increased in pH 4.3 solution, $Ca^{2+}$, $PO{_4}^{3-}$, $F^-$ consumption in experimental solutions, weight increment of HA seed, and fluoride ratio in crystallized samples were increased. There were significant differences among the groups (p < 0.05). But in pH 7.0 solution, these phenomena were not significant. In pH 7.0 solutions, analyses of crystallized samples showed higher Ca/P ratio in higher fluoride concentration. There were significant differences among the groups (p < 0.05). But in pH 4.3 solution, there were not significant differences in Ca/P ratio. Conclusions: Crystal growth in pH 4.3 solutions was superior to that in pH 7.0 solutions. In pH 4.3 solutions, crystal growth increased with showed in higher fluoride concentration up to 4 ppm.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.20 no.6
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• pp.550-554
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• 2007

Large and single-grain Y-Ba-Cu-O(YBCO) bulk superconductors have been fabricated by using a seeded infiltration and growth method. $Y_2BaCuO_5$(Y211) precursor pellets and $YBa_2Cu_3O_x$(Y123) liquid source pellets were prepared using commercial powder and were processed by infiltration and growth method to achieve low pore and high trapped field property. The superconductor properties of the single crystal are measured and analyzed in relation with the density and size of the Y211 particle in the Y123 matrix. An optimum processing condition is suggested based on the analyzed results.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.10 no.4
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• pp.279-285
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• 2000

High quality crystals of $YMnO_3$, which is interested in non-volatile memory device application, were grown by the floating zone method. Optimum condition for powder synthesis was established to be $1200^{\circ}C$ for 10 hrs and optimum condition for sintering of $YMnO_3$feed-rod was established to be $1500^{\circ}C$ for 10hrs respectively. It was found from non-seeded growth experiment that $YMnO_3$crystal was grown preferentially to the [1010] orientation. The $YMnO_3$single crystal, which was grown to the direction of perpendicular to C-axis, was typically 5mm in diameter, 50 mm in length and showed dark-blue color.

• Progress in Superconductivity and Cryogenics
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• v.21 no.3
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• pp.27-31
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• 2019

Large grain YBCO bulk superconductors are fabricated by the top-seeded melt growth (TSMG) or top-seeded infiltration growth (TSIG) method. Both growth methods use at least one of $YBa_2Cu_3O_{7-{\delta}}$, $Y_2BaCuO_5$, $BaCuO_3$ pre-reacted precursor powders. However, the synthesis of the pre-reacted powders includes multiple calcination runs which are cost-bearing and time-consuming. In this work, we report the successful growth of single-domain YBCO bulk superconductors directly by using the powder compact that has been pressed from the mixture of $Y_2O_3$, $BaCuO_3$ and CuO powders without any intermediate grinding step. Single-domain YBCO bulk superconductor has been also prepared by using $Y_2O_3$, $BaO_2$ and CuO powders without intermediate grinding step. Investigations on the trapped magnetic field and microstructure of the melt-processed specimen show that the elimination of the repeated processes of calcinations and pulverization has hardly affected on the crystal growth and the magnetic properties of the grown YBCO bulk superconductors. However, it is thought that the presence of residual carbon affects on the size of Y211 particles in melt-processed YBCO bulk superconductor.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.32 no.6
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• pp.516-521
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• 2019

The top seeded solution growth (TSSG) method is an alternative technique to grow high-quality SiC crystals that has been actively studied for the last two decades. However, the TSSG method has different issues that need to be resolved when compared to the commercial SiC crystal growing method, i.e., physical vapor transport (PVT). A particular issue of the TSSG method of results from the presence of liquid droplets on the grown crystal that can remain even after crystal growth; this induces residual stress on the crystal surface. Hence, the residual droplet causes several unwanted effects on the crystal such as the initiation of micro-cracks, micro-pipes, and polytype inclusions. Therefore, this study investigated the formation of the residual droplet through multiphysics simulations and lead to the development of a liquid droplet removal method. As a result, we found that although residual liquid droplets significantly apply residual stress on the grown crystal, these could be vaporized by adopting thermal annealing processes after the relevant crystal growing steps.

• Carbon letters
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• v.15 no.3
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• pp.151-161
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• 2014

Exceptional progress has been made with chemical vapor deposition (CVD) of graphene in the past few years. Not only has good monolayer growth of graphene been achieved, but large-area synthesis of graphene sheets has been successful too. However, the polycrystalline nature of CVD graphene is hampering further progress as graphene property degrades due to presence of grain boundaries. This review will cover factors that affect nucleation of graphene and how other scientists sought to obtain large graphene domains. In addition, the limitation of the current research trend will be touched upon as well.

• Progress in Superconductivity
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• v.14 no.1
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• pp.39-44
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• 2012

The fabrications condition and superconducting properties of top-seeded melt growth (TSMG) processed $GdBa_2Cu_3O_{7-y}$ (Gd123) bulk superconductors were studied. Processing parameters (a maximum temperature ($T_{max}$), a temperature for crystal growth ($T_G$) and a cooling rate ($R_G$) through a peritectic temperature ($T_P$) for the fabrication of single grain Gd123 superconductors were optimized. The magnetic levitation forces, trapped magnetic fields, superconducting transition temperature ($T_c$) and critical current density ($J_c$) of the Gd123 bulks superconductors were estimated. Single grain Gd123 bulk superconductors were successfully fabricated at the optimized processing condition. The $T_c$ of a TSMG processed Gd123 sample was 92.5 K and the $J_c$ at 77 K and 0 T was approximately $50kA/cm^2$. The trapped magnetic field contour and magnetic levitation forces were dependent on the top surface morphology of TSMG processed Gd123 samples. The single grain Gd123 samples, field-cooled at 77 K using a Nd-B-Fe permanent magnet with 5.27 kG and 30 mm dia., showed the trapped magnetic field contour of a single grain with a maximum of 4 kG at the sample center. The maximum magnetic levitation forces of the single grain Gd123 sample, field-cooled or zero field-cooled, were 40 N and 107 N, respectively.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2007.06a
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• pp.243-243
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• 2007

We have studied the electrical properties and microstructure of $(Y_{0.5}Nd_{0.25}Sm_{0.25})Ba_2Cu_3O_y[(YNS)-123]$ Oxides by rod-type seeded melt growth process(RSMG) in air atmosphere. Rod-type $NdBa_2Cu_3O_y${Nd-123) seed crystals made a extrusion process method, were used for achieving the ab-plane alignment having large grains perpendicular to the center of (YNS)-123 samples. The observations using SEM and TEM micrographs of the melt-textured (YNS)-123 samples revealed that the nonsuperconducting $(Y_{0.5}Nd_{0.25}Sm_{0.25})Ba_2Cu_3O_y[(YNS)-211]$ inclusions are uniformly distributed in the superconducting matrix. The microstructure and electrical properties were investigated by XRD, SEM, TEM and DC SQUID magnetometer. The sample showed a sharp superconducting transition at 90 K. The magnetization values of the (YNS)-123 sample exhibited the enhanced electrical properties, compared with $YBa_2Cu_3O_y$(Y-123) sample.

• Proceedings of the Korea Institute of Applied Superconductivity and Cryogenics Conference
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• 2003.10a
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• pp.93-95
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• 2003

YBa$_2$Cu$_3$O$_{x}$ (Y123) single crystal was grown by TSMG (top seeded melt growth) method. Physical properties of Y123 single crystal were dependent on the shape and distribution of Y2BaCuOx (Y211) in it and on the oxygenation temperature and the holding time. In this work, It was investigated to an optimal oxygenation condition and a dependence of melting temperature and holding time on physical properties. The optimal oxygenation condition was found that it was heat-treated for 30 hours at 45$0^{\circ}C$, Also it was found that the critical current density and the size of Y211 were increased with the melting temperature and the holding time.e.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.32 no.5
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• pp.212-217
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• 2022

Large thermal stress due to the difference between silicon carbide and graphite's coefficients of thermal expansion could be formed during crystal growing process of silicon carbide (SiC) at high temperature. The large thermal stress could separate the SiC seed crystals from graphite components, which bring about the drop of the seed crystal during crystal growth. However, the bonding properties of SiC seed crystal module has hardly reported so far. In this study, SiC and graphite were bonded using 3 types of bonding agents and a three-point bending tests using a mixed-mode flexure test were conducted for the bonded samples to evaluate the bonding characteristics between SiC and graphite. Raman spectroscopy, X-ray Photoelectron Spectroscopy, and X-ray Computed Tomography were used to analyze the bonding characteristics and the microstructures of the SiC-graphite interfaces bonded with the bonding agents. As results, an excellent bonding agent was chosen to fabricate SiC seed crystal module with 50 mm in diameter. An SiC single crystal with 50 mm in diameter was successfully grown without falling out during top seeded solution growth of SiC at high temperature.